The Thirteenth Tribe by Arthur Koestler is a meticulously researched book, advancing the controversial thesis, that European Jews and their descendants -- known as Ashkenazi Jews -- are not descended from the Israelites of antiquity, but from a group of Khazars, a people originating in the Caucasus region (historical Khazaria), who converted to Judaism in the 8th century and later migrated north and westwards into current Northern and Eastern Europe (Russia, Hungary, Ukraine, Poland, Belarus, Lithuania, Germany and other places outside the Caucasus region).
Koestler stated that part of his intent in writing this uncomfortable and unorthodox (politically incorrect) book, was to defuse anti-Semitism, by undermining the identification of European Jews with the ancient Jews of the Bible, rendering anti-Semitic epithets, such as "Christ killer" inapplicable. Arthur Koestler himself was a Hungarian Ashkenazi Jew by ancestry and a self-described secular Zionist, who supported the nationhood of Israel based on modern international law, not biblical terms.
The 'Thirteenth Tribe' by Koestler inspired another controversial book called The 'Invention of the Jewish People' (Hebrew: מתי ואיך הומצא העם היהודי?, Matai ve’ech humtza ha’am hayehudi?, literally When and How was the Jewish People Invented?) a book on the historiography of the origins of the Jewish people by Israeli professor Shlomo Sand, a Tel Aviv University historian and lecturer. 'Invention of the Jewish People' postulates similar controversial claims as 'Thirteenth Tribe'.
Other Controversial Books About Jewish History and Anti-Semitism